


Sins of Three

by iinoyb



Category: Undertale (Video Game)
Genre: Blow Jobs, Daddy Kink, Double Penetration, Ectobiology, Hand Jobs, Incest, M/M, Sexting, Threesome, Voyeurism
Language: English
Status: Completed
Published: 2017-08-28
Updated: 2017-08-28
Packaged: 2018-12-21 00:46:52
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 5,855
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11932830
Author URL: https://archiveofourown.org/users/iinoyb/pseuds/iinoyb
Summary: What happens in the family, stays in the family. (Repost from my old account)





	1. Distractions of the Pleasurable Kind

What sins could he possibly have committed in a previous life to justify this sort of punishment?

His magic sparked involuntarily, and Gaster had to use every inch of self-control in his possession to keep it from manifesting into something very embarrassing indeed.

The phone buzzes again, a small light flicking on to notify the royal scientist he just received another message.

With a small sigh and a darting look around the room, making sure none of his lab assistants noticed anything out of the ordinary, he looked down at his phone again, desperately trying to play it cool.

Trying to ignore the building heat in his bones and the slightly heavy pants his breathing is beginning to develop.

It's another photograph, of course. A close-up of... Holy fuck.

Two cocks rubbing together, pre-cum already dripping from the tips. A large skeleton hand is wrapped around them, edges slightly blurred in an unmistakable movement.

Gaster hasn't a doubt in the world as to whose genitalia are currently occupying his phone screen, as if the bright orange and blue colors weren't a dead give away.

He grits his teeth, noticing the caption Sans has ever so cheekily provided. "Wish you were here ;)"

Those two are going to be the death of him.

It had started with a text as well.

"We're bored."

Gaster had merely frowned, sending back a quick: "Aren't you two old enough to entertain yourselves?"

When Sans had answered after a long pause with a simple "ok", he should have known his eldest what up to something.

And that something apparently was driving his father completely insane.

The first picture had been rather innocent, just the two of them together on the bed. Gaster's bed, for some reason. As if that wasn't suspicious enough...

The subsequent pictures had involved less and less clothing, until there came the admittedly very arousing image of both his boys sprawled out naked on the sheets, a heavy blush of anticipation already on both their faces, looking like some kind of sinful window display.

It was at this sight, that Gaster had regained enough sense to send a: "What do you think you are doing?"

His sons had promptly responded with: "Entertaining ourselves."

This came with a picture of a blue tongue licking alluringly over a long skeleton neck. Papyrus's face was bright orange, eyes closed in apparent bliss, an expression Gaster himself had had the privilege of provoking on the younger's features on quite some occasions.

It didn't help in the slightest that his brain was providing the little whines of pleasure that were certain to accompany that appearance.

He had tried ignoring the slow build of pressure at his pelvis, his churning magic adamant in knowing how to best resolve the situation, but this latest picture really made it hard to keep doing so.

But he couldn't go home. No matter how much Gaster might have wanted to get to his boys ASAP and join in on the fun (oh, and how he would make them regret ever sending him these pictures. He would have them both begging and moaning and-)

There was a bulge in his black dress pants, barely concealed by his lab coat anymore, just the thought of the things he could be doing right now enough to slip the tiny vestige of control he had left.

There was no choice, Gaster simply could not work like this.

Trying desperately to keep the calm and collected look on his features, he quickly made his way to the nearest bathroom (thank god for monsters with a bladder that actually needed these kinds of facilities) and locked the door tight.

Almost immediately he unbuttoned the pants constricting his member, hissing at the pleasurable sensation caused by the enhanced magic flow, the cock getting impossibly even harder.

It was an awkward position, sitting on the lidded toilet, legs opened as far as they could go with the trousers constricting his ankles, black turtleneck bunched up to his breastbone, allowing his hand to hover over the sensitive ribs, brushing them gently in an effort to elevate part of the pent up arousal.

It didn't do much more than take the sharp edge of, but even this made him hiss in a pleasure almost bordering pain.

His unoccupied hand groped for his phone again, grunting upon seeing there were three more new messages, all from that same number.

A blue cock getting almost entirely swallowed up by an eager Papyrus, marmalade tinged drool dripping from the corner of his mouth. Sans's hands were evidently shaking when he took this one, the image slightly blurry and at an unsteady angle.

In the follow-up message, Sans has brought one hand down, fingering his own ribs eagerly. Gaster mimicked the motion on his own body, effortlessly imagining it is him with Papyrus between his hips, his son chocking on his considerable girth.

Almost without conscience thought, his voice changes from incoherent groans and needy gasps into actual words.

"Ah... y-yes... Pappy, you're so good at this." He manages out, knowing how much his youngest son would love the praises.

His hand wanders down to his dark purple ectodick, encircling it and rubbing slowly up and down, giving little twists at the tip that made his entire body shudder in ecstasy.

He barely has enough presence of mind to flick to the most recent message, grunting breathlessly in confusion as it seems to be nothing but a black screen.

His movements don't slow down, his arousal now a pleasant burn encompassing his entire being, not nearly enough to tip him over the edge, but just enough to look into the abyss.

That's when it hits him... It's a video. His fingers almost tremble too much for him to actually operate the device, but as soon as he find the play button, the room is filled with the sound of needy gasps and moans.

The image is shaky, almost making it impossible for Gaster to tell what's going on, but the filthy noises alone leave nothing to the imagination.

Staring at the screen through half-lidded eyes, he's barely able to make out Papyrus, lying on his back now, as his smaller brother straddles his hips, pushing and thrusting in an uneven rhythm.

The younger's orange cock is being deftly stroked by small hands, expertly spreading glistening pre cum all over the length.

"Sa-Sans.. P-Please.. I ne-AH" Sans shifted his position slightly, pushing in again and hitting that spot inside his brother's pelvis that was about the only thing that could effectively shut Papyrus up, reducing him to uttering desperate sounds and gasps instead.

His hand shoots up, grasping Sans's arm roughly, the other coming around to lay over his face, muffling the whines and pleas.

Sans only thrusts harder, grunting at the sensation of his brother's magic enveloping his own cock, tighter than it had any right to be.

"Come on, Pap.." He managed out after a moment, sounding absolutely horny, only turning Gaster on even more. "Make th-those beautiful sounds for dad now..."

That's what did it for poor Gaster.

The phone fell to the floor clattering, screen now facing downwards, but speakers still filling the room with those delicious moans.

He picked up the pace, the slick sound of his palm moving over pre-cum smeared ecto-flesh echoing of the walls, chasing that peak of pleasure that felt incredibly close now.

His minds eye was filled with images of what could be happening, if only he had the possibility of going home and joining his boys.

The thoughts of his member pushing into a tight conjured hole, thrusting hard and fast, making even somebody like Sans lose his composure, motions so eager they would shake his eldest son in such a way even Papyrus would be able to feel it, still being fucked by his elder brother even as Sans himself was being taken.

Gaster's free hand braced against the wall as the world narrowed down to that single thought, before rapidly exploding into a mixture of magic and pleasure and too much need, thick ropes of purple colored cum erupting from his cock.

When he came to himself again, the room was quiet, the video evidently having come to an end somewhere in his excitement. Only his harsh panting reverberating off the walls now.

Trying desperately to steady his breathing, Gaster waited until his magic had retreated back into itself, leaving behind only a faint, pleasurable buzzing that would most likely linger for some time to come, to remind him of his shameful activity.

The mirror showed his face was heavily flushed, dark purple a stark contrast to the pale white of his skull, as the royal scientist set about straightening his clothes and making himself look presentable again.

At last, he picked up the forgotten cellular device, frowning when he noticed there had been another message.

"Hope you enjoyed yourself, daddy ;)"

Gaster huffed indignantly at the smiley face and typed a fast response.

"There will be punishment when I come home."

The other scientists barely looked up as Gaster re-entered the lab, though some had given him a weird look upon noticing which room he came out of, seeing as he did not posses a bladder.

He settled back at his desk, pulling out his phone again, this time intent on turning it off, to avoid another such distraction.

There was one final text from his sons.

"We'll be eagerly awaiting your return."


	2. Sharing the Fun

**Summary for the Chapter:**

> Sans & Papyrus POV

Sans rolls over in his brother's lap slightly, stretching his legs languidly over the couch cushions, head resting on the other's pelvis.

Papyrus raises his arms to accommodate the fidgeting, eyes still glued to the television screen, displaying some kind of Mettaton rerun.

With a small grunt, Sans pulls the arms back down, liking the way they almost subconsciously hold on to him, as if to prevent him from falling off the sofa.

"I'm bored..." He drones, observing the pristine white of their ceiling. Papyrus hums something in response that might mean anything.

The smaller skeleton grumbles slightly at being ignored, fishing his cell phone out of his pocket and bringing it up to his face.

"I'm going to tell dad.." He hums, phalanges quickly working the keyboard to send the text.

This does catch his younger brother's attention.

"Don't-" Papyrus begins, but Sans holds up the phone to show him the message has already gone out.

"Too late." Sans shoves the cell down his pocket again, throwing his brother a meaningful look. "I just told him we're bored."

Papyrus goes to cross his arms, but since Sans is still holding on to them, he's unable to do so.

"I'm not bored, the Great Papyrus always has things to do."

"Is that right, bro? Well, _I_ am bored..." Sans shifts again, now positioning himself almost entirely in the taller skeleton's lap, effectively trapping the other's body beneath his.

"And I'm also horny." He adds in a husky tone, that immediately has Papyrus's cheekbones turn orange in response.

The younger brother averts his eyes, trying to formulate a decent response but ending up with an incoherent mumble instead. Sans grins at him.

"Come on, Pappy." He almost whines, knowing that the tone is likely to drive Papyrus up the wall. "I'm certain that the great Papyrus can cure my boredom."

Sans has started to slowly grind his pelvis downwards while talking, and he can feel the magic tension in the air rising with every thrust, his own soul burning in his rib cage.

There is a small buzz in his pocket and he pulls the phone out again, expecting to see some chiding response from their father to his earlier message.

When he sees what Gaster actually sent, he turns the screen towards his brother again.

"Entertain yourselves." He says, as if Papyrus can't read for himself.

The taller skeleton has turned a delicious shade of orange by now, head tilting slightly downward in embarrassment. "hmm- I guess..." He mutters almost too quietly, but Sans hears.

He bends forward to bring their mouths together, already summoned tongues rubbing each other as he grinds harder, feeling the beginning of some other magical appendages in the heat between their hips.

Upon pulling back, Papyrus has a distinctly dazed look on his face, some orange and blue saliva dribbling from the corner of his mouth, and Sans thinks it's a beautiful sight.

"It's almost a shame father isn't here..." Papyrus mumbled absentmindedly, eyes falling on the phone abandoned on the armrest somewhere along the way. He bends forward for another kiss, but Sans pulls back, a sudden idea taking shape in his mind.

"Just because he isn't here, doesn't mean he can't share the fun."

Papyrus shoots him a confused look, especially as Sans starts to extract himself from their comfortable position, his lap suddenly feeling unbearably empty.

"Come on." Sans urges, deliberately pocketing his phone and tugging on his younger brother's arm to make him come with.

Moments later they find themselves in their father's bedroom. Papyrus looks around, feeling beset with both confusion and curiosity.

Especially as Sans starts pulling his hoodie and shirt of, then proceeding to take a picture of himself bare chested.

"Strip." He says, with a gesture at his brother, and Papyrus finds himself almost instantly obeying the command, even as he's questioning it.

"Why are we undressing in father's bedroom?" He asks automatically, while Sans also takes a photo of him, then starts typing something on the phone.

"Because we're giving dad a show." The older brother hums, now also starting to remove his lower layers.

When both brothers are completely naked, their arousal already showing itself as two brightly colored members that faintly light up the room, Sans pull Papyrus to the king sized bed and motions for him to lay on it.

He takes more photos, making sure to save these particular images for himself also, instead of just sending them off to the by now probably very frustrated royal scientist. Then he joins his brother on the bed and takes some more.

Papyrus is about as aroused as one can get by now, not 100% certain why they are doing this, but the sinfulness of it all definitely edging him on. Sans is busy trying to keep a straight face as he poses for the pictures, resisting the urge to break out laughing at the silliness.

Satisfied that their father has got the full view of what is proceeding in his bedroom, Sans crawls over to Papyrus with a wicked grin.

"I think that's enough previews." He smirks, before engaging his brother in some more kissing, grinding their hips together once more.

The removal of their clothes makes an enormous difference, soon both are moaning as their dicks slide roughly together.

Papyrus reaching down to grasp them both and rub quickly, the sound of bone on ecto-flesh filling the room. Sans reaches for his phone yet again and takes some trembling pictures, sending them of to their father with a witty caption for good measure.

Poor Gaster must be crawling up the wall by now.

With a small gasp, Sans can feel himself getting dangerously close, and he urgently grabs his brothers wrist to stop the delicious friction.

"Nh-P-Paps... I think we can do better than this, right? For father." He manages, suppressing the hiss at the loss of movement.

He isn't sure why Papyrus takes this to mean he should start sucking Sans off, but he does, going down on him faster than ever before.

Sans moans loudly, head falling back and eye sockets half-closed at the feeling of his brother swallowing him down, tongue swirling around the head.

His hands clasp involuntarily, phalanges squeezing the phone tightly, before he raises it and barely manages to keep making footage.

The new angle provides an almost first-person view for whomever views the pictures, and Sans can only imagine what their father must be thinking right now.

Would he still be sitting at his desk, desperately trying to hide his arousal from his fellow scientist? Or maybe he would look for a secluded place to relieve himself, talk about getting indecent at the workplace.

Sans definitely pegs Gaster as the latter type.

One hand snakes down to rub his ribs, the camera now trembling so badly the pictures might be completely ruined, but he couldn't care less.

Not when the amazing wet heat around his member, eagerly bobbing up and down, is pushing him closer and closer to the edge once more.

It's truly amazing what magic can accomplish.

For the second time, Sans shoots out a hand to stop his brother's ministrations, and Papyrus pulls back with an eager smile, always happy when he can reduce his usually composed brother to a needy mess.

Sans smirks again. Two can play that game...

He pushes forward, hand splayed against his brother's rib cage, softy shoving him onto his back.

Papyrus automatically opens his legs in anticipation, feet already bracing against the soft blankets beneath.

Sans doesn't keep him waiting.

The first push in is slow, magic rushing to accommodate and adjust the foreign invasion. He waits until his brother settles, squirming slightly from feeling so full.

When the pelvis beneath him stills, Sans grasps it with eager hands and thrusts, hard.

Papyrus almost yelps, hands shooting up to grasp his brother's elbows, eye sockets screwing shut at the sensation.

Sans keeps going, the sounds his little brother are making quickly changing from small cries to full out mewling, hips thrusting down to meet Sans every time he pushes forward.

With the last presence of mind he still holds on to, the older brother quickly grabs his phone, switching it to video mode and adjusting it in such a way that it might film what they are doing, without him having to keep holding it.

The image quality and angle will most likely leave something to be desired, but Sans is sure Gaster will get the idea.

With that taken care of, Sans concentrates on the task of reducing his brother to a begging mess with vigor.

One hand still braced firmly against the other's pelvis, his other encircles the neglected orange member between them, rubbing it eagerly.

"Sa-Sans.. P-Please.. I ne-AH" Papyrus tries, but his brother is way ahead of him, shifting their position as to hit the younger skeleton's conjured prostate dead on.

The words get stuck in his throat and he ends up making gasping sounds instead, one hand still grasping his brothers elbow firmly, while the other arm shoots up to cover his face in embarrassment at the lewd sounds he's making.

Sans responds by thrusting deeper, the tightness engulfing his cock now bordering on the unbearable.

"Come on, Pap.." He grunts out, needing noticeable effort to still make a coherent sentence himself. "Make th-those beautiful sounds for dad now..."

The words are what do it for his brother, and Papyrus's entire body tenses as he comes, orange splattering the bed and his own rib cage. Sans keeps his hand going, making sure his baby brother is thoroughly spent, before grasping at the pelvis again and really bearing down on the body beneath him.

Papyrus makes a desperate sound, over-stimulation making his entire body tremble with each thrust, and the sight is enough to make Sans come undone, grunting as he fills his brother with his release.

When he regains his composure enough to actually think Sans fumbles for the phone, stopping the recording and barely able to send out another text to their father.

He feels Papyrus shift underneath him, trying to get into a more comfortable position now that their magic has dissipated, leaving them feeling tired but sated.

Sans rolls to his side, snuggling up against his brother, phalanges still working the keyboard of his phone. He opens the text as soon as it comes in, and a loud giggle escapes him.

"What's that?" Papyrus asks, voice still an octave higher than normal.

"It's father." Sans hums, showing the screen to his brother. "When he comes home, we better be ready for round two."

* * *


	3. Lessons Learned

**Summary for the Chapter:**

> The disciplining

This had been the longest workday Gaster had ever experienced in his entire live.

And that was coming from the man who has to take part in the monthly overview meeting at the royal labs.

After his little... break, Gaster had thrown himself back into his research with renewed vigor.

He had actually gotten quite a bit of work done after that. Maybe the unorthodox stress relief had been a benefit, though he would rather not mention that to his children.

His children, who had started this in the first place. Who needed to be taught a lesson.

Every time he shifted in his chair, a small wave of pleasure ran through him. It was residue magic that didn't dissipate as quickly as might have been practical. At least it didn't manifest into any unfortunate... appendages.

It just refused to let him forget what he had done. And what he had promised, as soon as he got home.

Monster biology could be so damn inconvenient at times. Gaster just hoped nobody noticed.

* * *

He closed the door behind him with a weary sigh, glad to be home. For various reasons, that was.

His sons where nowhere to be seen, and the royal scientist reveled in the momentary respite.

He loved his creations, he really did. But they could become quite wearisome at times.

They were his entire world. His magnum opus, his greatest achievement, whatever you may want to call it.

And yet... sometimes they drove Gaster to absolute desperation... in the best and worst of ways.

"Ah, father. You're home." While he stood busy lost in thought, the very subject of his reveries had entered the hallway. Papyrus smiled at him so sincerely, Gaster couldn't help but smile back.

Papyrus had that effect on many people.

"How was your day?" The young skeleton asked innocently. Gaster wasn't sure if he was acting or not. For all the demure air Papyrus seemed to radiate, their father knew from first hand experience how indecent his youngest son could really be if he set his mind to it.

"Quite well, despite some unexpected... interference." He answered, keeping his face straight.

"Well, I hope you got your work done regardless." Papyrus started making his way to the kitchen as he spoke and Gaster followed in his wake.

Sans was at the table, nasal bone deep in some book or another. The cover declared it to be quantum physics, but Gaster knew better than to take that at face value.

"I was just finishing our diner." Papyrus announced proudly, face brightening in anticipation.

Gaster was fairly certain what it was. "Spaghetti!" What a surprise.

"How was your day, then?" Gaster asked them nonchalantly while eating.

"Uneventful." Sans immediately answered, with a completely straight face.

"We have not done anything out of the usual." Papyrus was a bad liar, face already tinging orange from that one sentence, but Gaster decided not to comment.

If this was how they were going to do it, two could play that game.

"I see." He counted the seconds, making sure the silence between his words stretched for the ideal amount of time. "That is peculiar to say the least."

He didn't continue right away and noticed both their eyes flicker to him, then to each other, in turn. He kept his mouth shut, pretending he didn't notice.

"What makes you say that, father?" Papyrus asked at last, not dealing well with the silence.

"Well... You two seem to be completely oblivious, but I am of the opinion you acted very troublesome today."

Papyrus began sputtering and blushing even harder. The poor boy was really not well-suited for these kinds of games, though he liked going along with them just fine.

Gaster had already deduced the entire thing had been Sans's idea.

His eldest son glanced at him from across the table with a slightly mischievous grin. "I am sure we don't know what you are talking about."

"I am sure you need some punishment."

"I am sure you wouldn't punish us if we don't know what we've done wrong." Sans sat back slightly as he said that. "That wouldn't be very fatherly of you."

"I see." Gaster pretended to consider this revelation. "In that case, I should be responsible for educating you properly."

* * *

"If I remember correctly, you were not wearing any clothes."

Even Sans's cheeks colored at the tone of voice Gaster was employing now. He liked to call it his 'authoritative scientist voice', but Sans would just call it sexy.

They were in their father's room now, just like a few hours ago when Sans had got the bright idea of starting this debacle.

Well, it was partly Papyrus's idea, if anyone cared to ask. Though that may seem hard to believe for some people.

Sans had been horny, Papyrus had been willing, and somehow some innocent kisses and snuggles had escalated into heavy petting and panting.

Which was when his younger brother had carelessly mentioned how nice it would be if their father was with them.

They had just wanted to include Gaster in the fun.

Somehow it led to them now, standing at their father's bed, being asked to strip by that sinfully deep demanding voice, that really didn't take no for an answer.

Talk about escalation.

"Good." Gaster commented when his boys followed his command immediately. So eager to please, were they now?

He pulled up a chair from beside his desk, sitting himself down and allowing his eyes to hover over the two bare bodies before him.

So different and yet so similar, and both perfect in his humble opinion. Yes, he had done an excellent job on these two.

Sans tried to look defiant but his entire face was turning blue under the heavy scrutiny from his father, and Papyrus was even fidgeting nervously.

There wasn't much to see as far as naked skeletons were concerned, not when magic had not stirred to supply interesting... additions, yet.

But the way Gaster looked at them. Like he would happily devour both of them. The burning intensity of somebody utterly and completely pleased with the sight before him. It heated the entire room somehow.

"Well..." Gaster made a vague hand gesture toward the bed. "You were not standing around idly in the footage."

His boys observed each other silently for a second, both fully aware of what they had been doing back then.

Gaster was just starting to think they wouldn't do it, that maybe he had reasoned their motives wrong, when Sans turned and reached up, engaging his taller brother in a heated kiss.

Papyrus hesitated for the briefest of moments, but Sans was already allowing his hands to start roaming his brother's body, stroking the sensitive spine with gentle motions.

The two got utterly lost in the sensations quickly, allowing Gaster to just sit back and enjoy the show.

Magic was beginning to stir in the air, anticipation of what was ahead slowly rising.

Gaster's magic heated up faster than ever just watching his two boys enjoy each other so fully.

It was one of the most arousing things to see for him: his sons, his creations, HIS-

One soul in two bodies eagerly grasping at the chance to be whole again, even if it was for only a moment.

The poetic beauty might seem silly to some, but for the royal scientist who caused it, it was the most beautiful thing in the world.

The way blue and orange magic began to intermingle, blending effortlessly and filling the air with a dull glow. Gaster felt his own soul brighten in response, and it didn't take much effort at all for him now to summon a nice, thick member for himself to stroke.

Sans and Papyrus had gone from kissing and stroking to rutting incredibly fast, must have something to do with young monster's libido, their own magic genitalia brightening up the room as well.

Sans hissed as his brother rubbed the both of them in one hand, friction causing small sparks of pleasure to shoot through his body.

He remembered the text messages. The video. Knowing what was yet to come somehow made it better and worse at the same time.

The thought had barely crossed his mind or Papyrus was descending on him, wet heat engulfing his cock in one go.

Sans moaned and threw his head back at the sensation. His brother seemed quite eager at swallowing him whole, head bobbing up and down fast.

"A-h.. Ahn, Pap, I'm-" His cock was released with an obscene pop. Sans looked down into those bright eyes, his younger brother staring up at him questioningly.

Before he could say anything, Gaster was besides the bed, penis hanging out of the front of his unzipped pants obscenely.

Weren't he so busy trying not to cum before the script demanded it, Sans might have found the sight hilarious.

"Keep going." Gaster said, looking down at them with glee. Sans shivered beneath that gaze, but was reduced to moaning and grasping the sheets again as Papyrus returned to his previous occupation with zeal.

Gaster was gone again, and Sans had a second to wonder where the oldest skeleton had gone when he felt the sensation of his cock going impossibly even deeper down his younger brothers throat.

Papyrus gagged but didn't pull back, just kept going. Sans opened his eyes, mind clouded by an odd combination of intense pleasure and confusion.

It was then that he noticed his father again. He was still standing by the bed but... Oh god.

Gaster was sunken deep into Papyrus's rear, trusting a steady rhythm, grasping the young skeleton's pelvic bone to keep him still.

Every time their father moved forward, Papyrus chocked a bit more on Sans's cock, making the later cry out at the pleasure.

"That's what you get for lying to your father." Gaster addressed his youngest son, thrusting extra hard on each syllable for added emphasis.

Papyrus could barely grunt in response, eyes scrunched close as he was taken from both sides.

This position, while certainly pleasurable for his boys, would bring them no closer to a real climax, just as Gaster had intended.

Meanwhile, the sensation of tight heat wrapping around his cock in the most delicious manner brought him closer and closer to the edge.

Just a little more-

Gaster grunted in satisfaction as his orgasm ripped through him, thrusting in one last time while spurting his load.

Papyrus mewled a bit at the sudden feeling of being filled, but couldn't make much noise with his older brother's cock still deep down his throat.

Gaster pulled out with a sigh, appreciating his handy work.

"Very good, Papyrus. I think you have learned your lesson, haven't you." He laid his hand on the youngest skull with a contrite smile, loving the feel of heated bones beneath his palms.

Papyrus blushed even brighter orange, if at all possible, sitting back up and finally able to use his voice again. "Y-Yes, father."

"Good boy." Gaster felt the body underneath his hand shiver at the compliment. So responsive...

"Now for your brother."

The gaze Gaster sent his way could only be described as predatory, and Sans was filled with a renewed form of tension.

The kind that made his soul flare that much brighter and his magic flow faster because it knew he was fucked. In the good sense of the word.

"Get on your hands and knees."

Sans had never obeyed more rapidly in his life. He might have found this troublesome, was it not for the fact that he really rather get screwed right now. Literally.

Somehow his father was hard again, and in an instant, he was lining himself up and pushing in.

Sans could only gasp as the considerable girth breached him, bringing with it pain, but also so much pleasure. Especially as his father started moving, pulling out almost completely before pushing back in sharp and fast.

He grunted as Gaster picked up the pace, trusting at in steady strokes, hissing at the slight burn as he was still sensitive from already having cum once.

Suddenly, Sans felt arms encircle his torso and pull him up, the cock inside him reaching even deeper than before.

He glanced through slitted eyes to see Papyrus still on the bed also, pleasuring himself eagerly.

There was something deliciously lewd about his younger brother stroking himself while watching Gaster fuck him.

Still not as lewd as Gaster's next question. "No need to do that yourself, Papyrus. Won't you join? Your brother still has room."

Gaster pulled at Sans's torso some more, so he was almost lying back in his father's lap, openly exposed to his brother. Papyrus hesitated.

"I- I don't kn-" He began, but Sans interrupted him by reaching his hand out and pulling his brother closer.

"Ngh- Y-yes... Pap, please. Yes-" He pleaded. The building pleasure running through him was already unbearable. He needed more.

Papyrus didn't need to be told twice. It took a bit of effort to find a position that would work, but then there was the feeling of something else sliding inside him, beside the thing already filling him to the brim.

Magic rushed to accommodate the new situation, easing the pain into a slight burn into a satisfying thrill into pure ecstasy.

He felt full. Fuller than ever before. Fuller than he thought possible.

But it felt good. Great, even. Fucking amazing, to be honest.

Sans nuzzled his head against his brothers collarbone, gasping and licking and biting just to occupy his mouth, to keep the constant stream of groans and whimpers from pouring out instead.

He was close, but there was no way in the world to articulate this. Instead Sans let it sweep him away, his cock trapped between his own body and that of his brother erupting, cum staining their chests.

Sans smothered the scream by biting into his brothers neck, immediately feeling the taller body tense up at the sensation. A second later he was being filled by something warm and wet.

The world narrowed to this particular moment and nothing more...

It took him a minute to regain his senses. Sans was lying on the bed, half splayed on top of his equally debauched looking baby brother.

Gaster had pulled out also and stood besides the bed again. By the sheer feeling of it, he had not been far behind Papyrus, and Sans felt filled to the brim with brightly colored release.

He loved it.

He was dimly aware of Gaster talking to him.

"I hope the two of you have learned your lesson about distracting me while at work?"

"Certainly." Sans managed, though his voice sounded slightly hoarse from the eager noises it had been making up until now. "It's a good way to get a great fuck."

Gaster simply rolled his eyes at him and left the room.

This might be a lesson that needed to be repeated a few time over to truly stick...

**Author's Note:**

> Also feel free to visit [my Tumblr](https://iinoyb.tumblr.com/about), I take requests!


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